The terrible thing about worrying about it coming back is that, [email redacted] it, it does sometimes (3 times over 10 years for me). However, if you try to keep your mind on other things (work, family, etc), you can push it away for awhile. And the "awhiles" gradually become longer and longer.
This may be sort of dumb, but I found playing computer games like Freecell helped. You are just sort of mindlessly focused on the game for awhile and when you stop, you are on to the next thing, not the cancer thought. There is always gonna be that pain or bump that you think, oh it's cancer, but as time goes on, you can just laugh at yourself. Remember, doctors in training end up believing they have all these wierd diseases when they are learning all the symptoms of things! You have to stop and say, now really, what are the odds of that truly happening???? what is a more likely explanation?
Each time you are up for a recheck, you'll worry. But each time you are clear, you'll think, by golly, I made it this far so I think I can make it even farther.